.netcore 文件上传转为base64位字符串

　　.netcore文件上传Api接口，和正常的webForm提交类似，只是用postman测试接口时，记得给form表单命名，否则获取上传文件数量一直为0

　　后端代码

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using MyApiCommon;

namespace MyApi.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class FileController : ControllerBase
    {

        [HttpPost]
        [Route("postfile")]
        public